• Chemical evidence of steroids in sediment that are found in modern sponges

• Accepted fossils from Ediacaran period (pre-Cambrian, ~600mya)
  • mollusks, cnidarians and sponges

• Animals then diversify across Paleozoic, Mesozoic and Cenozoic
  • in both aquatic and terrestrial environemnts
  • punctuated by mass extinctions

• All share 3 traits

• All animals, except sponges, have:

1. Nerve cells called neurons
2. Muscle cells

• Animals are incredibly diverse
  • 35 major phyla
  • 1/3 are marine only
  • most phyla have marine members

• 95% of known animal species

• Occupy every habitat on Earth

• Small to huge (colossal squid)

• Groupings characterized by tissue layers,symmetry and unique structures

• Most ancestral animal group
  • marine
  • adults do not move, larva have flagella
  • filter feeders
  • hermaphroditic (alternate sexes)
  • lacks symmetry in body plan

• Lots of cells, but no tissue layers
  • produce many antibiotics

• Share similarities with protist Chonaflagellates
  • feed using cells called choanocytes

• Animals except sponges are considered “True Animals”
  • contain tissues

• Animals except sponges are considered “True Animals”
  • contain tissues

• First lineage to diversify were Cnidarians
  • corals, hydras and jellyfish
  • pre-Cambrian origins

• Diploblastic and radial symmetry
  • motile and sessile (non-moving)
  • medusa or polyp forms

• Corals have symbiotic relationships with single-celled algae

• Triploblasty = 3 germ/tissue layers

• Complete digestive tract (most groups)
  • mouth and anus connected by tube

• Bilateral = symmetrical in 2 halves

• Triploblasty = 3 germ layers

• Complete digestive tract
  • mouth and anus

• Bilateral = symmetrical in 2 halves

• 3 major clades of bilaterians

1. Lophotrochozoa
2. Ecdysozoa
3. Deuterostomia

• Lophophore: crown of ciliated tentacles for feeding

• Trophophore: distinctive larval stage
  • beating cilia
  • cylinder body

• This group is falling apart with new molecular-based phylogenies
  

• Animals with cuticle
  • shed tough external coat
  • shed as grow; molting; ecdysis

• 8 total phyla
  • more species than all other groups

• 2 major phyla

1. Nematoda (roundworms)
2. Arthropods (mostly insects)

• Cylinder bodies from 1mm to 1m

• Aquatic, soil, plant tissues, animals tissues
  • many parasitic species (crop pests)
  • humans are host to ~50 species!

• Longitudinal muscles; thrashing motion

Share many developmental characteristics with more complex animals, including humans

• A billion billion arthropods estimated
  • 1 million species described
  • nearly all habitats on Earth

• Segmented body, hard exoskeleton, jointed appendages
  • likely led to success

• Early arthropods (Trilobites) had little variation in body plan

• Evolution selected for functional body regions
  • head, thorax, abdomen
  • each with specialized functions